spruce up

Make neat and trim, as in She spruced up the chairs with new cushions. This idiom originated in the late 1500s as simply spruce but had acquired up by 1676.

Definition: make neat, well-groomed
Antonyms: dirty, mess up

The verb has 2 meanings:

Meaning #1: make neat, smart, or trim
  Synonyms: spruce, titivate, tittivate, smarten up, slick up, spiff up

Meaning #2: dress and groom with particular care, as for a special occasion
  Synonyms: spruce, slick up, smarten up